This disclosure relates to containers produced from polymeric materials and designed for packing comestibles and the like. More particularly, this invention relates to containers which are used to pack foods which have been retort processed for purposes of sterility. A container of this type and a method for its manufacture are disclosed in U.S. Ser. No. 059,374-MULTILAYER CONTAINER AND METHOD OF MAKING SAME and apparatus therefore is disclosed in U.S. Ser. No. 059,375-APPARATUS FOR MAKING A MULTILAYER INJECTION BLOW MOLDED CONTAINER; those applications are assigned to the same assignee as the present application.
In the past, multilayer blow molded polymeric containers have been suggested including those with barrier layers to reduce the permeation of oxygen through the wall of the container. The food or beverage packed therewithin is thus protected against oxidation. The problem of oxygen permeation is well known and it is known that permeation can be reduced by a suitable barrier material. Moreover, such materials have been used or suggested in a multilayer construction and have been used in connection with oxygen scavenging systems in order to absorb any oxygen which might pass through the barrier or remain in the head space above the packed and processed food or beverage. More particularly, Valyi U.S. Pat. No. 4,048,361 discloses a food container formed with a barrier material inside of which is a carrier layer containing a "getter". The getter may be an absorbent for any gas which permeates the barrier layer. An alternate approach of Valyi includes a barrier layer on both sides of the carrier layer whereby oxygen leaving the food or coming from the outside will be slowly absorbed by the getter. The Valyi patent specifically discloses antioxidants and container shape and construction, but is more general as regards other getters.
An early patent to Vijlbrief, U.S. Pat. NO. 4,586,514 discloses the use of antioxidizing agents mixed within a plastic barrier layer of a container to reduce the permeation of oxygen to the oxidizable material such as beer within such a container.
The U.S. Pat. No. 3,429,717 to Cook discloses a barrier of Saran.RTM. flexible film sandwich such as is used to wrap food with an antioxidant uniformly distributed in a solvent between the layers of Saran.RTM.. The antioxidant selected for use by Cook depends upon the film as well as the product to be contained in the light and heat condition to which the package will be exposed.
Yoshikawa teaches in U.S. Pat. No. 4,113,652 that the amount of ammonium salts or water in an oxygen scavenger comprising an alkaline metal sulfite, a ferrous compound and water can be adjusted to lengthen the period before the oxygen scavenger becomes effective. That is to say that, the addition of more water or ammonium salts to the oxygen scavenger will extend the period of latency. Yoskikawa only teaches a period of latency up to fifty hours. As will be appreciated when the thrust of the present disclosure is fully understood, such a latent period is impractical from the standpoint of commerical reality for a food container.
Various oxygen scavengers are also known in the art. An early teaching is the Loo et al patent U.S. Pat. No. 2,825,651 which discloses a dry oxygen remover system which includes hydrates, for example, an anhydrous sodium sulfite catalyzed by copper sulfate pentahydrate. Such an oxygen remover is included as a pellet inside of a protective package and is placed in the container head space. The problem of practicing the Loo et al patent are pointed out in the Yoshikawa patent.
More germane to multilayer containers is Scholle U.S. Pat. No. 4,041,209 which discloses an aqueous solution of a reducing sulfite salt which can be directly oxidized disposed between a high barrier outer layer and a low barrier inner layer thus permitting the oxygent to permeate outward from the head space to react with the sulfite salt while retarding oxygen flow from outside inward. However, an oxygen scavenger system must remain passive or inert in order to preserve its oxygen scavenging capacity until such time as the food is sealed within the container. Many times a container may sit empty in a warehouse for several months before it is used. None of the prior art containers and oxygen scavenging systems disclose a means by which the passivity of the scavenger contained in a multilayer container will be maintained until such time as the oxygen scavenger is most beneficial.